The present invention relates to a vehicle travelling along a lead line preinstalled in a floor or on the ground, and a method of steering the same.
Conventional vehicles are divided into three types: a front wheel steering type, a rear wheel steering type, and a front- and rear-wheel interlocking steering type, as shown in FIGS. 1A to 1C. While the front wheel steering type vehicle is travelling, as shown in FIG. 1A, the front wheels 12 are so controlled that the vehicle travels along the lead line 10. The rear wheels 14 are fixedly directed toward a straight forward direction parallel to the lead line. The steering direction and degree of the front wheels 12 are determined by the direction and absolute value of a positional error (deviation) detected by a detector 18 mounted at the front end of the vehicle 16. On the other hand, in the rear wheel steering type vehicle shown in FIG. 1B, the front wheels 12 are fixedly directed toward a straight forward direction, and the rear wheels 14 are steered in accordance with the output from the detector 18. In the case of the front- and rear-wheel interlocking steering type vehicle shown in FIG. 1C, the front wheels 12 are steered in the same manner as those of the front wheel steering type vehicle, and the rear wheels 14 are steered in the same manner as those of the rear wheel steering type vehicle, such that the front wheels 12 are steered at a given positive angle with respect to a straight forward direction and the rear wheels 14 are steered at an equal but negative angle with respect to the straight forward direction.
The common factor in these conventional vehicles lies in the fact that only one detector 18 is arranged to detect a deviation from the lead line 10. Therefore, a problem as shown in FIG. 2 occurs. In particular, when the detector 18 is exactly aligned on the lead line 10, further steering cannot be performed even if the vehicle 16 is not parallel to the lead line 10. Therefore, the vehicle 16 crosses the lead line 10, and travels in a zigzag manner, as shown in FIG. 3. The vehicle 16 cannot be completely aligned with the lead line 10 in a short period of time, resulting in inconvenience. This is because the angle of inclination of the vehicle 16 to the lead line is not corrected.